The thermal fuse is also called a thermal fusible cutout, which is usually mounted in electrical appliances that are prone to generating heat. If the appliance fails and generates heat, and if the temperature exceeds normal temperature ranges, the thermal fuse will automatically fuse to cut off the appliance's power supply to prevent the electric appliance from catching fire. In recent years, the thermal fuse has been mounted on most household appliances that primarily operate as sources of heat, such as rice cookers, electric irons, and electric furnaces. When internal parts stop working, the thermal fuse can cut off the power supply to prevent the appliance from further internal damage to the appliance, and to avoid causing a fire of the appliance and anything surrounding the appliance. Fuses are well known in the prior art, and thermal fuses work as a path of the power in the circuit. The thermal fuse does not melt until the current in the circuit exceeds thermal fuse's rated value. The thermal fuse has a relatively lower resistance, a relatively smaller power loss and a relatively lower surface temperature. In case of an abnormal temperature due to a failure of an electrical appliance, the thermal fuse melts and thus cuts off the power supply of the circuit.
The thermal fuse plays a role in protection from excessive temperatures in the power supply circuit. If the temperature of the region where the thermal fuse is located reaches the fusing-off temperature of the fusible alloy wire inside the thermal fuse, then, the fusible alloy wire shrinks towards the leads at both ends to cut off the circuit with the help of the fusing agent. The current circuit is thereby cut off to prevent other components in the circuit from being further damaged by the excessive temperature. Thus, the thermal fuse is applied in many circuits that need protection from excessive temperatures. Different circuits have different requirements for the thermal fuse.
In a direct current circuit with a high voltage level of 400V or above, during the process of fusing the fusible alloy wire of the traditional thermal fuse, an arc is generated due to the low shrinking speed of the fusible alloy wire and the small gap between the two leads, so that the circuit cannot be cut off in time. The circuit may be destroyed and/or catch fire due to the occurrence of the arc, as well as the high-temperature of the circuit. Thus, if the existing thermal fuse is used in a direct current circuit with a voltage level of 400V or above, the existing thermal fuse not only fails to cut off the circuit in time to protect the circuit, but also may cause additional problems.